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      <b>stelab_c</b> </td>
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            <small>
              <a href="#Procedure">Procedure<br></a>
              <a href="#Abstract">Abstract<br></a>
              <a href="#Required_Reading">Required_Reading<br></a>
              <a href="#Keywords">Keywords<br></a>
              <a href="#Brief_I/O">Brief_I/O<br></a>
              <a href="#Detailed_Input">Detailed_Input<br></a>

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              <small>               <a href="#Detailed_Output">Detailed_Output<br></a>
              <a href="#Parameters">Parameters<br></a>
              <a href="#Exceptions">Exceptions<br></a>
              <a href="#Files">Files<br></a>
              <a href="#Particulars">Particulars<br></a>
              <a href="#Examples">Examples<br></a>

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              <small>               <a href="#Restrictions">Restrictions<br></a>
              <a href="#Literature_References">Literature_References<br></a>
              <a href="#Author_and_Institution">Author_and_Institution<br></a>
              <a href="#Version">Version<br></a>
              <a href="#Index_Entries">Index_Entries<br></a>
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<h4><a name="Procedure">Procedure</a></h4>
<PRE>
   void stelab_c ( ConstSpiceDouble   pobj[3],
                   ConstSpiceDouble   vobs[3],
                   SpiceDouble        appobj[3] ) 
</PRE>
<h4><a name="Abstract">Abstract</a></h4>
<PRE>
 
    Correct the apparent position of an object for stellar 
    aberration. 
 </PRE>
<h4><a name="Required_Reading">Required_Reading</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Keywords">Keywords</a></h4>
<PRE>
 
    EPHEMERIS 
 

</PRE>
<h4><a name="Brief_I/O">Brief_I/O</a></h4>
<PRE>
 
    VARIABLE  I/O  DESCRIPTION 
    --------  ---  -------------------------------------------------- 
    pobj       I   Position of an object with respect to the 
                   observer. 
    vobs       I   Velocity of the observer with respect to the 
                   Solar System barycenter. 
    appobj     O   Apparent position of the object with respect to 
                   the observer, corrected for stellar aberration. 
 </PRE>
<h4><a name="Detailed_Input">Detailed_Input</a></h4>
<PRE>
 
    pobj        is the position (x, y, z, km) of an object with 
                respect to the observer, possibly corrected for 
                light time. 
 
    vobs        is the velocity (dx/dt, dy/dt, dz/dt, km/sec) 
                of the observer with respect to the Solar System 
                barycenter. 
 </PRE>
<h4><a name="Detailed_Output">Detailed_Output</a></h4>
<PRE>
 
    appobj      is the apparent position of the object relative 
                to the observer, corrected for stellar aberration. 
  </PRE>
<h4><a name="Parameters">Parameters</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Exceptions">Exceptions</a></h4>
<PRE>
 
   1) If the velocity of the observer is greater than or equal 
      to the speed of light, the error SPICE(VALUEOUTOFRANGE) 
      is signaled. 
 </PRE>
<h4><a name="Files">Files</a></h4>
<PRE>
 
    None. 
 </PRE>
<h4><a name="Particulars">Particulars</a></h4>
<PRE>
 
    Let r be the vector from the observer to the object, and v be 
        -                                                    - 
    the velocity of the observer with respect to the Solar System 
    barycenter. Let w be the angle between them. The aberration 
    angle phi is given by 
 
         sin(phi) = v sin(w) / c 
 
    Let h be the vector given by the cross product 
        - 
 
          h = r X v 
          -   -   - 
 
    Rotate r by phi radians about h to obtain the apparent position 
           -                      - 
    of the object. 
 </PRE>
<h4><a name="Examples">Examples</a></h4>
<PRE>
 
    In the following example, <b>stelab_c</b> is used to correct the position 
    of a target body for stellar aberration. 
 
       /.
       (Previous subroutine calls have loaded the SPK file and 
       the leapseconds kernel file.) 
       ./
      
       /.
       Get the state of the observer with respect to the solar 
       system barycenter. 
       ./
       <a href="spkssb_c.html">spkssb_c</a> ( idobs,  et, &quot;J2000&quot;, sobs ); 
 
       /.
       Get the light-time corrected position `tpos' of the target
       body `targ' as seen by the observer. Normally we would
       call <a href="spkpos_c.html">spkpos_c</a> to obtain this vector, but we already have
       the state of the observer relative to the solar system
       barycenter, so we can avoid looking up that state twice
       by calling <a href="spkapo_c.html">spkapo_c</a>.
       ./
       <a href="spkapo_c.html">spkapo_c</a> ( targ, et, &quot;j2000&quot;, sobs, &quot;lt&quot;, tpos, &amp;lt );

       /.
       Apply the correction for stellar aberration to the
       light-time corrected position of the target body.
       The corrected position is returned in the argument
       `pcorr'.
       ./
       <b>stelab_c</b> ( tpos, sobs+3, pcorr );
 

    Note that this example is somewhat contrived. The sequence
    of calls above could be replaced by a single call to <a href="spkezp_c.html">spkezp_c</a>,
    using the aberration correction flag &quot;lt+s&quot;.

    For more information on aberration-corrected states or
    positions, see the headers of any of the routines

       <a href="spkezr_c.html">spkezr_c</a>
       <a href="spkez_c.html">spkez_c</a>
       <a href="spkpos_c.html">spkpos_c</a>
       <a href="spkezp_c.html">spkezp_c</a>

 </PRE>
<h4><a name="Restrictions">Restrictions</a></h4>
<PRE>
 
    None. 
 </PRE>
<h4><a name="Literature_References">Literature_References</a></h4>
<PRE>
 
    1) W.M. Owen, Jr., JPL IOM #314.8-524, &quot;The Treatment of 
       Aberration in Optical Navigation&quot;, 8 February 1985. 
 </PRE>
<h4><a name="Author_and_Institution">Author_and_Institution</a></h4>
<PRE>
 
    N.J. Bachman    (JPL)
    H.A. Neilan     (JPL) 
    W.L. Taber      (JPL) 
    I.M. Underwood  (JPL) 
 </PRE>
<h4><a name="Version">Version</a></h4>
<PRE>
 
  -CSPICE Version 1.0.1, 8-JAN-2008 (NJB)

      The header example was updated to remove references
      to <a href="spkapp_c.html">spkapp_c</a>. 

  -CSPICE Version 1.0.0, 22-OCT-1998 (NJB)

      Based on SPICELIB Version 1.0.2, 10-MAR-1992 (WLT)
   </PRE>
<h4><a name="Index_Entries">Index_Entries</a></h4>
<PRE>
 
   stellar aberration 
 </PRE>
<h4>Link to routine stelab_c source file <a href='../../../src/cspice/stelab_c.c'>stelab_c.c</a> </h4>

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   <pre>Wed Jun  9 13:05:31 2010</pre>

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